Actuator

ABSTRACT

An actuator for transducing a rotational movement into a linear movement, which comprises: 
     a drive motor generating the rotational movement; 
     a first input gear connected to an output shaft of the drive motor; 
     a first output gear engaging with the first input gear at a first gear ratio and having an external thread portion; 
     a second output gear engaging with a second input gear at a second gear ratio and having an inner thread portion meshing with the external thread portion; 
     an output member connected to the second output gear and generating the linear movenment; and 
     the first and second gear ratios being different from each other.

This is a continuation of application Ser. No. 07/508,897, filed Apr.12, 1990, now U.S. Pat. No. 4,129,273, issued Jul. 14, 1990.

BACKGROUND OF THE INVENTION

The present invention relates to an actuator for transducing arotational movement into a linear movement.

Actuators, wherein a rotational movement generated by an electric orfluid pressure motor is transduced into a linear movement by means of aball screw and so on, have been conventionally known.

However, in such conventionally known actuators, transmission gearratios cannot be changed in accordance with the external load by asimple mechanism.

Accordingly, it has been required to develop an actuator whereintransmission gear ratio can be changed by a simple mechanism inaccordance with the external load.

Further, the reducing gear ratios in such conventionally known actuatorsare small, and accordingly, the amount of linear movement per onerevolution of the motor is large. Therefore, a large motor has to beused so as to obtain a desired output force.

Accordingly, in the conventionally known actuators, there are problemsthat a large space is required for installing such a large motor, thatthe actuator is heavy because of such a large motor and that the cost ofthe actuator is expensive since such a large motor is expensive.

In order to overcome the above-mentioned problems, an attempt, whereinthe rotation of the motor is reduced by a gear train or an epicyclereduction gear disposed on an output shaft of the motor, has been doneso that the reduction gear ratio is made large, i.e., so that the amountof linear movement per one revolution of the motor is made small.

Further, according to the conventional actuators, in order to enhancethe reduction gear ratio at the rotational stage, it is necessary toprepare a set of gear trains wherein the diameters of the gears arelargely different or to dispose various stages of gear trains.Accordingly, a large space is still necessary, and the weight of theactuator is increased. In addition, there occurs a problem that theconstruction is complicated when an epicycle reduction gear is used.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an actuator by whichthe problems inherent to the conventionally known actuators can beovercome.

It is another object of the present invention to provide an actuator fortransducing a rotational movement into a linear movement which iscompact and light and by which a large reducing gear ratio can beachieved.

It is a still other object of the present invention to provide anactuator for transducing a rotational movement into a linear movement bywhich transmission gear ratios can be changed by a simple mechanism.

According to the first aspect of the present invention, theabove-described objects are achieved by an actuator for transducing arotational movement into a linear movement, which comprises:

a drive motor generating the rotational movement;

a first output gear driven by the drive motor at a first gear ratio;

a second output gear driven by the drive motor at a second gear ratio:

the first and second gear ratios being different from each other: and

an output member generating the linear movement in response to angulardifference between the first and second gears.

According to this aspect of the present invention, a differentialmechanism, which reduces the rotational movement of the drive means andwhich transmits it to the transducing means, is disposed between thedrive means and the transducing means, and accordingly, the actuator canbe compact and can achieve a large reducing gear ratio.

According to the first embodiment of the present invention, thedifferential mechanism comprises:

a first output gear engaging with the first input gear at a first gearratio and having an external thread portion:

a second output gear engaging with a second input gear at a second gearratio and having an inner thread portion meshing with the externalthread portion; and

the first and second gear ratios being different from each other.

This embodiment is preferred since the actuator of the first embodimentcan be compact and can achieve a large reducing gear ratio.

According to the second embodiment of the present invention, thedifferential mechanism comprises:

a first output gear engaging with the first input gear at a first gearratio and having an external thread portion;

a second output gear engaging with the second input gear at a secondgear ratio and having a hollow portion;

the first and second gear ratios being different from each other: and

a summing block having an inner thread portion meshing with the externalthread portion of the first output gear and axially movably disposedwithin the hollow portion of the input gear.

This embodiment is preferred since the transmission efficiency betweenthe second output gear and the summing block can be enhanced.

According to another aspect of the present invention, an actuator fortransducing a rotational movement into a linear movement is provided,which comprises:

a drive means generating the rotational movement;

a transducing means transducing the rotational movement into the linearmovement;

an output means outputting the transduced linear movement; and

a reducing means disposed between the drive means and the transducingmeans and reducing the rotational movement and transmitting it to thetransducing means; and

a control means controlling connection between the drive means and thereducing means.

In the thus obtained actuators, transmission gear ratios can be easilychanged by controlling the connection between the drive means and thereducing means by means of the control means.

Further, in this aspect of the present invention, a differentialmechanism, which reduces the rotational movement of the drive means andwhich transmits it to the transducing means, is disposed as the reducingmeans between the drive means and the reducing means.

As illustrated in the third embodiment, which will be explained later,the present invention of this aspect is preferably constructed as anactuator for transducing a rotational movement into a linear movement,which comprises:

a drive motor generating the rotational movement;

an input gear shaft connected to an output shaft of the drive motor;

a first input gear shaft inserted onto the input shaft and a secondinput gear connected to the input gear shaft;

a clutch means controlling connection between the first input gear andthe input gear shaft;

a first output gear engaging with the first input gear at a first gearratio and having an external thread portion;

a second output gear engaging with the second input gear at a secondgear ratio and having an inner thread portion meshing with the externalthread portion;

an output member connected to the second output gear and generating thelinear movement; and

the first and second gear ratios being different from each other.

The thus obtained actuator is preferred because it can be compact andcan achieve a large reducing gear ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be explained in detail with reference tothe accompanying drawings which show some embodiments of the presentinvention and wherein:

FIGS. 1 to 3 are cross sectional views of the different embodiments ofactuators of the present invention, which embodiments are carried out asthe electric-mechanical actuators of control surface of an aircraft.

PREFERRED EMBODIMENTS

Some embodiments of the present invention, which are carried out in theelectric-mechanical actuators (EMA) of a control surface of an aircraft,will now be explained in detail.

FIG. 1 shows a first embodiment of the present invention. A housing 1,an end la of which is connected to an air frame (not shown), has anelectric motor 2, such as a servo motor or a stepping motor, mountedthereon, and both ends of an output shaft 6 of the motor 2 are rotatablysupported on the housing 1 by a pair of bearings 13.

The output shaft 6 has a first input gear 5 and a second input gear 7integrally formed therewith or disposed thereon.

According to this embodiment, the first and second input gears 5 and 7have the same diameters and the same numbers of teeth.

A first output gear 8, which engages with the first input gear 5, isrotatably supported on the housing 1 via bearings 14.

The second input gear 7 engages with a second output gear 9.

The front end (the right end in FIG. 1) of the first output gear 8projects like an hollow cylinder which has a ball screw 8a (an externalthread) formed on the outer periphery thereof. A second output gear 9has a hollow cavity 9a, which has a ball screw 9b (an inner thread)formed on the inner surface thereof. The ball screws 8a and 9b mesh witheach other via balls 10.

The second output gear 9 is formed in a long gear extending in an axialdirection so that it can move in an axial direction of the ball screws8a and 9b, and the second output gear 9 rotatably supports a piston 3via bearings 11 though it does not allow the piston 3 any movement in anaxial direction relative to the second output gear 9. A rod end 4 isintegrally connected to the piston 3 and constitutes an output end. Therotation of the piston 3 is prevented by connecting the rod end 4 to afinal controlling element, such as a control surface of an aircraft,which has to be moved linearly.

A detector 12 of the position of the piston 3 is disposed in the housing1 so that it locates within an elongated hole 8b formed in the firstoutput gear 8. The positional detector 12 of this embodiment is a linearvariable-differential transformer (LVDT).

The numbers of teeth of the first and second output gears 8 and 9 areslightly different, for example, the difference is one. Either one ofthem may be larger than the other. However, the moving direction of thepiston 3 relative to the rotational direction of the motor 2 may bealtered in accordance with the fact which number is larger than theother.

It is assumed that the numbers of both the first and second input gears5 and 7 are 12, that the number of the first output gear 8 is 48, andthat the number of the second output gear 9 is 49. When the motor 2 isrotated four revolutions, together with the first and second input gears5 and 7, the first output gear 8 rotates one revolution, while thesecond output gear 9 rotates 48/49 revolutions, and thus, the ballscrews 8a and 9b connected to the first and second output gears 8 and 9relatively rotates by the difference in revolutions, i.e., 1/49revolutions. As a result, the second output gear 9 axially moves by adistance, which is equal to lead length×1/49, together with the piston3.

More specifically, when the motor 2 rotates 4×49=196 revolutions, thepiston 3 moves by one lead of the ball screws 8a and 9b. The position ofthe piston 3 is fed back to the motor 2 by means of the positionaldetector 12.

As described above, the rotation of the motor 2 is reduced by thedifferential mechanism and then is transduced into the linear movementby the ball screws 8a and 9b.

A second embodiment of the present invention will now be explained withreference to FIG. 2. Similar to the first embodiment, a housing 1, anend 1a of which is connected to an air frame (not shown), has anelectric motor 2, such as a servo motor or a stepping motor, mountedthereon, and both ends of output shaft 6 of the motor 2 are rotatablysupported on the housing 1 by a pair of bearings 13.

The output shaft 6 has an input gear 15 integrally formed therewith ordisposed thereon. In this embodiment, the thickness of the input gear 15is made large, and a single gear is used, however, the gear may bedivided into two gears, i.e., first and second gears.

A first output gear 8 which engages with the input gear 15 is rotatablysupported on the housing 1 via bearings 14. Further, the input gear 15also engages with a second output gear 9. The second output gear 9 isrotatably supported by bearings 18 and 19.

The front end (the right end in FIG. 2) of the first output gear 8projects like an hollow cylinder which has a ball screw 8a (an externalthread) formed on the outer periphery thereof. A second output gear 9has a hollow cavity 9a.

A summing block 16 formed in a cylindrical shape is rotatably disposedwithin the hollow cavity 9a via ball spline 17 so that it can move in anaxial direction of the second output gear 9 though it is not allowed tobe relatively rotated relative to the second output gear 9.

A summing block 16 has a ball screw 16a (an inner thread) formed on theinner surface thereof. The first output gear 8 and the ball screws 8aand 16a mesh with each other via balls 10.

The front end portion of the summing block 16 rotatably supports thepiston 3 via a bearing 11 in such a manner that it does not allow thepiston 3 to move axially relative to the summing block 16.

Similar to the first embodiment, a rod end 4 is integrally connected tothe piston 3 and constitutes an output end. The rotation of the piston 3is prevented by connecting the rod end 4 to a final controlling element,such as a control surface of an aircraft, which has to be movedlinearly.

A detector 12 of the position of the piston 3 is a linearvariable-differential transformer (LVDT) similarly to the firstembodiment and is disposed in the housing 1 so that it locates within anelongated hole 8b formed in the first output gear 8.

Similar to the first embodiment, the numbers of teeth of the first andsecond output gears 8 and 9 are slightly different, for example, thedifference is one. Although either one of them may be large, the movingdirection of the piston 3 relative to the rotational direction of themotor 2 may be altered depending on the fact which number is larger thanthe other. The operation of the differential mechanism is similar tothat of the differential mechanism installed in the first embodiment.

Thus, the rotation of the motor 2 is reduced by the differentialmechanism, which comprises the first and second gears 8 and 9 and thesumming block 16, and then is transduced into the linear movement by theball screws 8a and 16a.

In the first embodiment, the second input gear and the second outputgear engage with each other and they move in an axial direction relativeto each other while they transmit their rotations therebetween.

Contrary to this, in the second embodiment, there is disposed thesumming block 16, which has the inner thread portion 16a engaging withthe external thread portion 8a of the first output gear 8, and thesumming block 16 is connected to the second output gear 9 via amechanism such as the ball spline 17, which moves relatively in an axialdirection while it transmits the rotation during its rolling contact.

As a result, the transmission efficiency of the second embodiment is notdecreased in case that the transmission efficiency of the firstembodiment is decreased.

The above-described explanations have been done with reference to theactuators installed in aircrafts. However, the present invention can beapplied not only to actuators used in aircrafts but also to actuators bywhich a rotational movement is transduced into a linear movement andwhich are widely used in various industrial fields.

According to the present invention, an actuator for transducing arotational movement into a linear movement is provided which is compactand light and by which a large reducing gear ratio can be achieved.

FIG. 3 shows a third embodiment of the present invention. A housing 1has an end 1a connected to an air frame (not shown) and has an electricmotor 2, such as a servo motor or a stepping motor, mounted thereon. Anend of an output shaft 6 of the motor 2 is rotatably supported on thehousing 1 by a bearing 15.

A first input gear 5 has cylindrical portions 5a projecting therefromand is loosely inserted onto the output shaft 6. The first input gear 5is rotatably supported on the housing 1 at the cylindrical portions 5a.A clutch brake 46 of an electro-magnetic type is disposed in the housing1 in such a manner that it faces the outer periphery of the cylindricalportion 5a of the first output gear 5.

The clutch brake 46 electro-magnetically connects the output shaft 6 tothe first input gear 5 or electro-magnetically disconnects the formerfrom the latter in accordance with an externally transmitted electricsignal. Further, the first input gear 5 is electro-magneticallyconnected to the housing by the clutch brake 46 when the clutch brake 46disconnects the output shaft 6 from the first input gear 5 so that therotation of the first input gear 5 is stopped.

The output shaft 6 has a second input gear 7 integrally formed therewithor disposed thereon at the right end thereof.

According to this embodiment, the first and second input gears 5 and 7have the same diameters and the same numbers of teeth.

A first output gear 8 engages with the first input gear 5 and isrotatably supported on the housing 1 via bearings 14. Further, thesecond input gear 7 engages with a second output gear 9.

The front end (the right end in FIG. 1) of the first output gear 8projects like an hollow cylinder which has a ball screw 8a (an externalthread) formed on the outer periphery thereof.

A second output gear 9 has a hollow cavity 9a, which bas a ball screw 9b(an inner thread) formed on the inner surface thereof. The ball screws8a and 9b mesh with each other sandwiching balls 10 therebetween.

The second output gear 9 is formed in a long gear extending in an axialdirection so that it can move in an axial direction of the ball screws8a and 9b. The second output gear 9 rotatably supports a piston 3 viabearings 3 though it does not allow the piston 3 any movement in anaxial direction relative to the second output gear 9.

A rod end 4 is integrally connected to the piston 3 and constitutes anoutput end. The rotation of the piston 3 is prevented by connection ofthe rod end 4 to a final controlling element, such as a control surfaceof an aircraft, which has to be moved linearly.

A positional detector 12 of the piston 3 is disposed in the housing 1 sothat it locates within an elongated hole 8b formed in the first outputgear 8. The positional detector 12 of this embodiment is a linearvariable-differential transformer (LVDT).

The numbers of teeth of the first and second output gears 8 and 9 areslightly different, for example, the difference is one, either one ofthem may be larger than the other, however, the moving direction of thepiston 3 relative to the rotational direction of the motor 2 may bealtered depending on which number is larger.

It is assumed that the numbers of both the first and second input gears5 and 7 are 12, that the number of the first output gear 8 is 48, andthat the number of the second output gear 9 is 49.

When the clutch of the clutch brake 46 is "off" due to the externalsignal, the input shaft 6 and the first input gear are disconnected fromeach other, and the first input gear 5 is secured to the housing 1 bymeans of the brake of the clutch brake 46. As a result, the rotation ofthe motor 2 is transmitted to the second input gear 7 and the secondoutput gear 9, and it rotates the ball screw 9b.

Contrary to this, due to the securing of the first input gear 5, boththe first output gear 8 and the ball screw 8a are also secured, andaccordingly, the rotation of the second output gear 9 generates axialdisplacement of the ball screw 9b. Thus, the piston 3 is linearly movedvia the bearing 11.

The transmission gear ratio becomes 12/49 when the first input gear 6 isdisconnected by the clutch brake 46.

In the meantime, when the clutch of the clutch brake 46 is "on" so thatthe input shaft 6 and the first input gear 5 are connected to eachother, operation is as follows.

When the motor 2 is rotated four revolutions, together with the firstand second input gears 5 and 7, the first output gear 8 rotates onerevolution, while the second output gear 9 rotates 48/49 revolutions,and thus, the ball screws 8a and 9b connected to the first and secondoutput gears 8 and 9, respectively, rotates relatively by the differencein revolutions, i.e., 1/49 revolutions. As a result, the second outputgear 9 axially moves by a distance, which is equal to lead length×1/49,together with the piston 3.

More specifically, when the motor 2 rotates 4×49=196 revolutions, thepiston 3 moves by one lead of the ball screws 8a and 9b. The position ofthe piston 3 is fed back to the motor 2 by means of the positionaldetector 12.

Thus, the rotation of the motor 2 is reduced by the differentialmechanism and then is transduced into the linear movement by the ballscrews 8a and 9b.

As described above, according to the present embodiment, in accordancewith the conditions of the clutch brake 46, two types of transmissiongear ratios can be obtained, i.e.,

differential transmission gear ratio=1/196 when the clutch is "on", and

one stage transmission gear ratio=12/49 when the clutch is "off".

The ratios can be freely set by altering the numbers of the teeth of thefirst input gear 5, the second input gear 7, the first input gear 8 andthe second output gear 9.

The above-described explanation has been done with reference to anactuator installed in an aircraft. However, the present invention can beapplied not only to actuators used in aircrafts but also to actuators bywhich a rotational movement is transduced into a linear movement andwhich are widely used in various industrial fields.

Further, although a differential mechanism including ball type externaland internal threads is exemplified as a reducing means, the reducingmeans of the present invention is not limited to the exemplified type.

According to the present invention, an actuator for transducing arotational movement into a linear movement is provided, which iscompact, light and inexpensive and by which transmission gear ratios canbe changed by a simple mechanism.

What we claim is:
 1. An actuator for transducing a rotational movementinto a linear movement, which comprises:a drive means generating saidrotational movement; a transducing means transducing said rotationalmovement into said linear movement; an output means outputting saidtransduced linear movement; and a reducing means disposed between saiddrive means and said transducing means and reducing said rotationalmovement and transmitting it to said transducing means wherein saidreducing means comprises a first input gear and said drive meansgenerates rotational movement through a second input gear; and a controlmeans controlling connection between said drive means and said reducingmeans.
 2. An actuator for transducing a rotational movement into alinear movement, which comprises:a drive motor generating saidrotational movement; an input gear shaft connected to an output shaft ofsaid drive motor; a first input gear inserted onto and connected ontosaid input gear shaft and a second input gear connected to said inputgear shaft; a clutch means controlling the connection between said firstinput gear and said input gear shaft; a first input gear engaging withsaid first input gear at a first gear ratio and having an externalthread portion; a second output gear engaging with said second inputgear at a second gear ratio and having an inner thread portion meshingwith said external thread portion; an output member connected to saidsecond output gear and generating said linear movement; and said firstand second gear ratios being different from each other.
 3. An actuatoras claimed in claim 1 wherein said first and second input gears aredisposed on the drive means.